sprintf in a loop with a file name

I lost on how to proceed. I need to save each iteration as its own png file:

Code:

for i=1:76
    mask=pixel_labels==(i);
    cluster=RGB.*uint8(mask(i));
    imagename=sprintf('Cluster%d.png',i);
    imwrite(cluster,imagename)
end

[madhan ravi]

And the above doesn’t do it?

[Adam Danz]

imwrite does not support writing of indexed PNG files that have insufficient colormap entries. If that's the case for your images, try using imwrite(A,map,filename)